1. Field of the Invention
The present invention relates to a method of controlling inclination angle of Fabry-Perot tunable filters.
2. Description of the Related Art
The Fabry-Perot tunable filter is constituted by arranging opposite a semitransparent mirror to be used as a fixed mirror, and a semitransparent mirror to be used as a movable mirror. And, a plural piezoelectric element is arranged with same interval on the semitransparent mirror to be used as the movable mirror, the inclination angle of the movable mirror is adapted to be able to change by making expand and contract the piezoelectric elements with the change of voltage.
This is for the reason that it is necessary to adjust so that the surface of the fixed mirror and the surface of the movable mirror become completely parallel state by controlling the inclination angle of the movable mirror, when the fixed mirror and the movable mirror are not assembled under the exactly parallel state. In case that the inclination angle of the movable mirror is to be changed, the amount of expansion and contraction of a plural piezoelectric element is adjusted suitably so that the movable mirror is rotated around a predetermined imaginary axis, thereby the movable mirror is adjusted so as to incline by a desired angle in the desired direction.
For example, in Japanese Patent No. 3039969, the control surface of Fabry-Perot resonator is supported by piezoelectric elements more than three, parallelism between the fixed surface and the control surface is adjusted by rotating the control surface to two axes met at right angles with each other on the control surface parallel to the fixed surface according to a displacement of the piezoelectric elements.
In this Japanese Patent No. 3039969, three piezoelectric elements are arranged so as to form a regular triangle as a top point the first piezoelectric element, at 120° interval, that is, equal space to the semitransparent mirror, and one of the two axes met at right angles, that is, Y axis is the first standard axis parallel to the semitransparent mirror and passing through the center of the semitransparent mirror and the attachment position of the first piezoelectric element, the other, that is, X axis is the second axis parallel to the semitransparent mirror, passing through the center of the semitransparent mirror and perpendicular to the Y axis. That is to say, the X axis passes through the center of gravity of three piezoelectric elements and is parallel to the line combining the second piezoelectric element and the third piezoelectric element.
And, in this Japanese Patent No. 3039969, when the fixed mirror and the movable mirror are not assembled with exactly parallel to each other, the movable mirror is adjusted so as to become parallel state to the fixed mirror by controlling its inclination.